An Amtrak police officer points to commuters chosen for random explosive screening to assist in increased security measures following fatal explosions in Boston, in New York's Penn Station, April 16, 2013. New York is on heightened alert after two bombs packed with ball bearings tore through crowds near the finish line of the Boston Marathon, killing three people and triggering a massive hunt for those behind an attack the White House said would be treated as "an act of terror". REUTERS/Lucas Jackson (UNITED STATES - Tags: CRIME LAW TRANSPORT)